In my U.S. Pat. No. 3,485,521 there is illustrated a seal of the padlock type, in which the body is formed of a synthetic organic plastic with a pair of apertures opening to one end of the body, and the shackle is formed of a U-shaped piece of wire having reverse bent end portions, which end portions, when inserted into the body openings, are locked therein by the end portion being maintained in a flexed condition so that the end of the reverse bent portion digs into the wall of the housing aperture.
Although the seal as illustrated in the above-identified patent has achieved considerable commercial success, it has been found that in some instances it has been possible to work an end of the shackle out of its aperture to enable the seal to be removed and re-assembled without leaving evidence of tampering.